There has hitherto been known an optically anisotropic film containing an organic dye having a sulfonic acid group.
This optically anisotropic film is obtained by coating a solution containing the foregoing organic dye and water on a base material, followed by drying.
The foregoing optically anisotropic film containing an organic dye having a sulfonic acid group is inferior in water resistant properties. For that reason, it is known that this film is subjected to a water resistant treatment.
Patent Documents 1 and 2 disclose that a film containing an organic dye having a sulfonic acid group is water-resistance processed by bringing it into contact with a solution containing a metal salt such as a barium salt.
In the water resistant treatment in each of Patent Documents 1 and 2, for the purpose of removing a metal salt remaining on the film after bringing the solution containing the metal salt into contact with the film, the surface of the film is cleaned with water.
However, when water is used as a cleaning liquid, there may be the case where a crack is generated in the film. Also, as described above, in the case where the film is formed on a base material, there is a concern that when water is used as a cleaning liquid, the film is partially separated from the base material.
Patent Document 1: JP-A-11-21538
Patent Document 2: JP-A-2007-241267